Synthesis and stereoselective halogenolysis of optically pure benzylstannanes.

In this work we show that lithium ortho-sulfinyl benzylcarbanions are highly efficient reagents for the synthesis of optically pure benzylstannanes by reacting with halotriorganyl tin (up to >98:2 dr). The stereoselectivity of these reactions is opposite to those observed with carbon electrophiles. Bromolysis of the obtained ortho-sulfinylbenzylstannanes with Br(2) in the presence of CuBr takes place in a highly stereoselective way (up to 90:10 dr) with retention of the configuration, which allows the synthesis of optically pure 2-sulfinylated benzyl bromides. Different experiments support the proposed mechanistic rationalization for both processes.